Recovery of fissile materials from nuclear wastes
A process for recovering fissile materials such as uranium, and plutonium, and rare earth elements, from complex waste feed material, and converting the remaining wastes into a waste glass suitable for storage or disposal. The waste feed is mixed with a dissolution glass formed of lead oxide and boron oxide resulting in oxidation, dehalogenation, and dissolution of metal oxides. Carbon is added to remove lead oxide, and a boron oxide fusion melt is produced. The fusion melt is essentially devoid of organic materials and halogens, and is easily and rapidly dissolved in nitric acid. After dissolution, uranium, plutonium and rare earth elements are separated from the acid and recovered by processes such as PUREX or ion exchange. The remaining acid waste stream is vitrified to produce a waste glass suitable for storage or disposal. Potential waste feed materials include plutonium scrap and residue, miscellaneous spent nuclear fuel, and uranium fissile wastes. The initial feed materials may contain mixtures of metals, ceramics, amorphous solids, halides, organic material and other carbon-containing material.
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1. A method for the conversion of radioactive waste and other waste material into glass comprising the steps of:
- a) providing a bath of molten B.sub.2 O.sub.3 and PbO;
- b) forming a molten dissolution glass comprising xPbO:B.sub.2 O.sub.3;
- c) adding said waste to said dissolution glass to form a molten glass/waste mixture, wherein metals and metal compounds in said waste are oxidized to yield metal oxides, molten lead is formed, noble metals are dissolved in said lead, and halogens are converted to lead halides which are gases at the temperature of the molten mixture;
- d) separating said gases from said molten mixture;
- e) contacting said gases with an aqueous scrubber solution of an alkali metal hydroxide to yield a soluble alkali metal halide and a lead-containing precipitate;
- f) separating said molten lead, containing dissolved noble metals, from said molten mixture;
- g) adding carbon to said molten mixture to remove lead oxide by converting it to lead and carbon oxides;
- h) removing said carbon oxides and said lead from said molten mixture to yield a glassy boron oxide fusion melt containing dissolved metal oxides;
- i) adding said fusion melt to an aqueous nitric acid solution wherein said fusion melt, including said metal oxides in said fusion melt, are rapidly and easily dissolved in said acid solution;
- j) separating and recovering metals from said acid solution; and
- k) converting said acid solution into a waste glass.
2. The method of claim 1 wherein said lead-containing precipitate is lead hydroxide and said hydroxide is returned to said molten dissolution glass/waste mixture.
3. The method of claim 1 further comprising processing said lead formed in steps (c) and (g) to separate and recover said noble metals, oxidizing said lead to lead oxide, and returning said lead oxide to said molten dissolution glass/waste mixture.
4. The method of claim 1 further comprising allowing said boron oxide fusion melt to solidify before adding it to said nitric acid solution.
5. The method of claim 1 wherein said waste contains metals or metal compounds of one or more of plutonium, uranium, and rare earths.
6. The method of claim 5 wherein step (j) further comprises separating one or more of plutonium, uranium and rare earths as nitrates, and recovering said plutonium, uranium and rare earths.
7. The method of claim 1 further comprising recovering boron oxide from said boron oxide fusion melt formed in step (h), and reintroducing it into said molten dissolution glass/waste mixture.
8. The method of claim 1 further comprising recovering boron oxide from a boric acid-nitric acid solution formed in step (j), and reintroducing said boron oxide into the glass/waste mixture.
9. The method of claim 6 wherein glass frit is added to a boric acid-nitric acid solution remaining after one or more of said plutonium, uranium and rare earths has been removed, to produce a waste glass suitable for storage or disposal.
10. The method of claim 8 further comprising adding glass frit to said boric acid-nitric acid solution to produce a waste glass suitable for storage or disposal.
11. The method of claim 9 wherein said glass frit is SiO.sub.2, and said waste glass is a borosilicate glass.
12. The method of claim 10 wherein said glass frit is SiO.sub.2, and said waste glass is a non-borosilicate glass.
13. The method of claim 1 wherein said steps (a) through (h) are carried out in a cold-wall glass melter.
14. The method of claim 1 wherein the mole ratio of PbO to B.sub.2 O.sub.3 is 2 to 1.
15. The method of claim 1 wherein said waste contains carbon-containing compounds, and said compounds are oxidized by said dissolution glass to form carbon oxides, and water.
16. The method of claim 5 wherein plutonium and uranium are separated from said acid solution by complexing them with tributylphosphate.
17. The method of claim 5 wherein plutonium and uranium are separated from said acid solution by ion exchange.
18. The method of claim 1 wherein said waste contains plutonium scrap and residue, spent nuclear fuel, and uranium fissile wastes.
19. The method of claim 1 wherein said PbO is present in at least a stoiciometric amount with respect to halogens in said waste material.
20. A method for recovering uranium and plutonium from plutonium residues, spent nuclear fuel, and uranium fissile wastes comprising:
- a) providing a bath of molten B.sub.2 O.sub.3 and PbO;
- b) adding a waste feed material comprising carbon-containing material, halides, and plutonium and uranium in metal or compound form, to said bath to form a molten mixture of dissolution glass and waste;
- c) oxidizing said waste feed material including said carbon-containing material, plutonium and uranium;
- d) precipitating molten lead which is formed by said step of oxidizing;
- e) converting said halides to lead halides which are gases at the temperature of said molten mixture;
- f) removing said gases to an aqueous scrubber solution of an alkali metal hydroxide, wherein lead hydroxide and alkali metal halides are formed;
- h) returning said lead hydroxide to said molten mixture;
- i) adding carbon to said molten mixture to convert said lead oxide to lead and carbon oxides;
- j) removing said lead from said molten mixture wherein a glassy boron oxide fusion melt containing oxides of plutonium and uranium is formed, said fusion melt being essentially devoid of halides and carbon-containing material;
- k) solidifying said glassy boron oxide fusion melt; and
- l) dissolving said fusion melt in nitric acid, and recovering plutonium and uranium.
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- Benedict, et al., Nuclear Chemical Engineering, McGraw-Hill, Inc., New York, pp. 461-463, 466-469, 1981 (No Month Available). Jensen et al, Recovery of Noble Metals from Fission Products, Nuclear Technology, vol. 65, pp. 305-324, May 1984. C. W. Forsberg et al., "Conversion of Radioactive and Hazardous Chemical Wastes into Borosilicate Glass Using the Glass Material Oxidation and Dissolution System", Waste Management, vol. 16, No. 7, pp. 615-623, 1996. (No Month Available). Charles W. Forsberg, "Recovery of Fissile Materials from Plutonium Residues, Miscellaneous Spent Nuclear Fuel, and Uranium Fissile Wastes", paper presented at the 1997 Annual Spring Meeting American Institute of Chemical Engineers, Houston, Texas, Mar. 9-13, 1997.
Filed: Nov 5, 1997
Date of Patent: Oct 5, 1999
Assignee: U. S. Department of Energy (Washington, DC)
Inventor: Charles W. Forsberg (Oak Ridge, TN)
Primary Examiner: Stanley S. Silverman
Assistant Examiner: Sean Vincent
Attorneys: Virginia B. Caress, William R. Moser, Paul A. Gottlieb
Application Number: 8/964,761